The present invention relates to an optical disk apparatus, an optical disk access method and an optical disk, and more particularly to those adapted for application to a disk recording/reproducing apparatus designed for mini disk (MD), compact disk (CD), digital video disk (DVD) and so forth. The present invention is so contrived that, when information of copyright is recorded by repeatedly forming local regions which cause greater changes in the return-light receiving result as compared with pits or marks, the existence ratio of such local regions in the circumferential direction of the disk is set to be less than 0.3, hence ensuring exact reproduction of the copyright information recorded like a bar code for example.
It is noticed recently that mini disk apparatus, which serve conventionally as optical disk apparatus, are diffused rapidly in use due to an advantage that music can be copied simply and easily from a variety of contents with prevention of deterioration in the tone quality. More specifically, in a mini disk apparatus, music information distributed through the Internet can be recorded on a mini disk for a test-listening, or music on a compact disk borrowed from a friend or the like can be recorded on a mini disk for a test-listening.
However, in such simplified easy copying achieved with prevention of any tone quality deterioration, there is possibility that, although a merit is attainable in enhancing the convenience for users, the profits of a copyrighter or a creater of the music may be impaired For this reason, various measures are discussed now for protection of copyrighters"" profits in the world-wide groups and forums such as RIAA (Recording Industry Association of America), SDMI (Secure Digital Music Initiative), CPTWG (Copy Protection Technical Working Group) and so forth.
As one of such measures, there is proposed a method which records music information after encrypting the same by copyright protective information unique to each recording medium. According to this method, when the music information has been copied onto another recording medium, it becomes difficult to decrypt the information since the copyright protective information is different in each recording medium individually, thereby preventing unlimited copy to consequently protect the copyrighters"" profits.
With regard to such copyright protective information recording system, there are proposed a method of forming a sector difficult to be accessed by users and recording copyright protective information in the sector, and a method of recording such information like a bar code by partially removing a reflective film with respect to recorded main data of pit rows (International Laid-open No. WO97/14144).
In the latter one of the above two methods for recording the copyright protective information like a bar code by partially removing a reflective film, a laser beam is modulated by a predetermined modulating signal and then is irradiated repeatedly onto an optical disk, wherein data to be recorded are processed through PE (Phase Encode) modulation to generate a modulated signal, thereby producing clock pulses from the reproduced signal and realizing reproduction of the data recorded like a bar code in unit of one bit.
In such bar-code recording based on the conventional method known heretofore, there exists a problem that the operation of an optical pickup is rendered unstable to consequently fail in exact reproduction of the copyright protective information.
More specifically, in the recording method mentioned above, the optical characteristic of an information recording film is changed locally and unreversibly by irradiation of a laser beam. Therefore, in the unreversible change of the optical characteristic derived from irradiation of a laser beam, a noticeable feature is such that the optical characteristic change on the information recording plane becomes great to eventually cause remarkable change in the quantity of return light obtained by irradiating the laser beam in a reproduction mode. Also in such bar-code recording, there is another feature that, in comparison with a case of using mark rows or the like, the local change extends over a relatively longer distance in the circumferential direction of the optical disk. And when accessing the region where the copyright protective information is recorded as mentioned, a time period, during which the return light of a sufficient quantity cannot be received in the optical disk apparatus, is rendered relatively longer to bring about a possibility of failure in executing proper focus control. And if such proper focus control is rendered difficult, it is considered that proper reproduction of the copyright protective information is also difficult in the optical disk apparatus.
It is an object of the invention to provide an optical disk apparatus, an optical disk recording method and an optical disk, wherein information of copyright can be reproduced exactly when such copyright information is recorded by repeatedly forming local regions which cause greater changes in the return-light receiving result as compared with pits or marks.
To achieve the above object, according to a first aspect of the present invention, there are provided an optical disk apparatus and an optical disk recording method, wherein a laser beam is irradiated to repeatedly form, in a predetermined area of an optical disk, local regions which cause greater changes in the return-light receiving result as compared with pits or marks, and information of copyright is recorded in such local regions. The existence ratio of the local regions in the circumferential direction of the optical disk is set to be less than 0.3.
According to a second aspect of the present invention, there is provided an optical disk wherein information of copyright is recorded in local regions which are formed repeatedly in a predetermined area of the disk by irradiation of a laser beam and cause greater changes in the return-light receiving result as compared with pits or marks, in such a manner that the existence ratio of the local regions in the circumferential direction of the optical disk is less than 0.3.
According to a third aspect of the present invention, there is provided an optical disk apparatus wherein copyright information recorded on an optical disk is reproduced through comparison of the sampling results obtained by sampling the return-light receiving result at predetermined timings.
With this configuration since the local regions causing great changes in the return-light receiving result are formed repeatedly in a manner that the existence ratio thereof in the circumferential direction of the disk is less than 0.3, even if a time period incapable of receiving the return light of a sufficient quantity is relatively long, it is possible to shorten such time period of an insufficient light quantity as a whole by comparison with the time period during which the return light of a sufficient quantity can be received. Consequently, it becomes possible to attain adequate setting to completely avoid undesired circumstances where proper focus control is rendered difficult, hence enabling exact reproduction of the copyright protective information.
Accordingly, the present invention can realize a satisfactory optical disk adapted for achieving certain reproduction of the copyright information.
Also according to the present invention, the copyright information recorded on an optical disk can be reproduced through comparison of the sampling results obtained by sampling the return-light receiving result at predetermined timings, so that even in case any change of a low-frequency signal level is generated in the return-light receiving result, a decision can be made as to the time point when the sampling result of the highest signal level has been obtained. Therefore, with application of the above to a case of recording the copyright information in local regions formed repeatedly to cause great changes in the return-light receiving result, it becomes possible to effectively avoid any harmful influence of the change of the low-frequency signal level even in case the 1-bit recording has a circumferentially long distance, hence realizing exact reproduction of the copyright information with certainty.